The invention relates generally to the field of suspension systems for vehicles. In particular, the invention relates to a magnetorheological fluid actuated damper for use in vehicular suspension systems.
Suspension systems are used in modern vehicles to tune the characteristics of the ride and handling of the vehicle. The suspension system in each type of vehicle is matched to the type of ride that the operator of that vehicle would prefer. Some vehicles have suspension systems that provide a smoother ride than others and some vehicles have tighter, more precise handling characteristics. More modern suspension systems often allow an operator to choose the type of ride for the vehicle. For example, an operator might desire a xe2x80x9csofterxe2x80x9d ride when driving over rougher terrain and a xe2x80x9charderxe2x80x9d ride with more precise handling when driving on smooth terrain.
A magnetorheological (xe2x80x9cMRxe2x80x9d) fluid is a substance that relies on a magnetically capable media compounded in a way that allows the substance to change form from a liquid state to a more viscous state. In one form, an MR fluid has a viscosity and consistency much like common motor oil. When a magnetic field is applied, however, the fluid changes form, becoming more resistant to shear force. This increase in viscosity results from a dipole moment introduced into magnetic particles suspended in the fluid from the magnetic field. The particles form chains, aligning in parallel to the magnetic field. The increase in viscosity depends on the strength of the field applied to the fluid and the size and quantity of the particles. This change in viscosity of the fluid takes place within milliseconds.
Because of the capability to change viscosity quickly and easily, MR fluids have been used to provide adjustable resistance in many types of systems. For example, U.S. Pat. No. 5,816,372 discloses a system for use in an exercise machine to control the resistance in exercise equipment. The system includes a spinning rotor within a housing and an MR fluid in place between the rotor and the housing. In order to increase the resistance a user feels while exercising, a magnetic field is applied to the MR fluid and the increased viscosity of the MR fluid makes it more difficult to rotate the rotor. A similar system is disclosed in U.S. Pat. No. 6,186,290 for use as a braking system.
MR fluids have also been used in telescopic dampers in vehicles. A telescopic damper can be filled with MR fluid to provide adjustable resistance to the vertical movement of the wheel of a vehicle. A telescopic damper utilizing MR fluid requires a substantial amount of MR fluid to be viable and a large magnetic field to operate. Another type of damper utilizing MR fluid is a rotary shock absorber of the type disclosed in U.S. Pat. Nos. 4,942,947 and 5,257,681. This type of shock absorber allows the dampening of relative movement between a blade attached to a shaft in connection with a wheel of a vehicle, and the housing around the blade. The system provides a means to apply an adjustable magnetic field to an MR fluid in the housing to control the movement of the blade in relation to the housing. It is desirable to further increase the adjustability of this type of vehicular dampening system while minimizing the cost of the system.
In one embodiment of the present invention, a magnetorheological fluid actuated damper is provided. At least a first and a second cylinder with the first cylinder positioned axially within the second cylinder are provided. A gap is formed between the cylinders. The second cylinder is mounted to a stationary mount of the vehicle chassis and a control arm is mounted at an end of the first cylinder. The first cylinder is mounted on bearings to allow it to rotate relative to the chassis. The gap between the cylinders contains a magnetorheological fluid having an adjustable viscosity in reaction to the application of a magnetic field. A magnetic field is generated over the fluid in the gap.
In a second embodiment of the present invention, a magnetorheological fluid actuated damper is provided. At least a first and a second concentric cylinder are provided and the first cylinder is mounted axially within the second cylinder so as to form a gap between the cylinders. The second cylinder is mounted to a stationary mount of a vehicle chassis and a control arm is mounted on an end of the first cylinder. The first cylinder is mounted on bearings to allow it to rotate relative to the chassis. The gap between the cylinders contains a magnetorheological fluid having an adjustable viscosity in reaction to the application of a magnetic field. A means for producing a magnetic field over the fluid in the gap is provided.
In a third embodiment of the present invention, a magnetorheological fluid actuated damper is provided. At least a first and a second concentric cylinder are provided and the first cylinder is mounted axially within the second cylinder so as to form a gap between the cylinders. The first cylinder is mounted to a stationary mount of a vehicle chassis and a control arm is mounted on an end of the second cylinder. The second cylinder is mounted on bearings to allow it to rotate relative to the chassis. The gap between the cylinders contains a magnetorheological fluid having an adjustable viscosity in reaction to the application of a magnetic field. A magnetic coil is in contact with at least one of the cylinders and the coil is attached to an electronic circuit allowing variation in current supplied to the coil to adjust the viscosity of the fluid.
In a fourth embodiment of the present invention, a magnetorheological fluid actuated damper is provided. At least three concentric cylinders defining gaps between them are provided. A first gap is defined between the first and the third cylinder and a second gap is defined between the second and the third cylinder. The third cylinder is mounted on bearings to allow rotation of the third cylinder relative to the first and second cylinders. The third cylinder is attached to a first end of a control arm at an end of the third cylinder such that oscillation of the control arm causes the third cylinder to rotate relative to the first and second cylinders. The first and second gaps between the cylinders are filled with a magnetorheological fluid and a coil capable of producing a magnetic field affecting at least one of the gaps to adjust the viscosity of the fluid is provided.
In a fifth embodiment of the present invention, a method for adjustably dampening the suspension system of a vehicle through the use of a magnetorheological fluid actuated barrel damper is provided. The method includes the steps of providing at least a first and a second concentric cylinder and positioning the first cylinder axially within the second cylinder so as to create a gap between the cylinders. A magnetorheological fluid is provided in the gap and the desired level of dampening is determined. Feedback is read from sensors on the vehicle and the viscosity of the fluid is controlled through the application of a magnetic field on the fluid such that the resistance to rotation of the rotatable cylinder changes in response to the change in viscosity of the fluid.